Some printers are designed such that the first and second print units are arranged and disposed along a medium conveying path of the printer. Each of the first and second print units may include a thermal head and a platen that are opposed to each other so as to be spaced apart from each other, and is configured to print information on a front surface and a rear surface of the medium respectively.
The thermal head may be elastically biased by means of an elastic biasing member such as a spring so that it is brought into pressure contact with the platen, and the medium passes between the thermal head and the platen.
However, conventionally, since the thermal head is brought into pressure contact with the platen by certain elastic biasing force, the thickness of the medium may not be constant along the conveying direction of the medium. For example, when an electronic tag for RFID is contained in label paper as a medium, a label paper portion bearing the electronic tag has increased thickness. Thus, when the label paper portion having the electronic tag contained therein passes between the thermal head and the platen, the tag could receive high impact, which may damage the electronic tag.